Add option to generate chained assertions

Enhancement

Use case:

* You have an object "objectA" of type ObjectA which contains (among other fields) a field objectB of type ObjectB
* To assert it, I do
```java
assertThat(objectA).hasFieldOfObjectA("field");
assertThat(objectA.objectB).hasFieldOfObjectB("fieldOfObjectB");
```
* I'd like to be able to assert like this:
```java
assertThat(objectA)
.hasFieldOfObjectA("field")
.withObjectB()
.hasFieldOfObjectB("fieldOfObjectB");
```
I already do that manually, but I think it could be useful to be able to add this behavior automatically.

What do you think?